This invention relates generally to multiple electric fuel metering systems and, in particular, to a multiple fuel manifold system and method for operating the same.
Attempts have been made to design fuel systems to minimize fuel consumption while maintaining high engine performance. One such attempt is shown in FIG. 1. Fuel metering system 10 may include a fuel supply 30, from which pump 40 may deliver fuel to a manifold 70 for distribution within a gas turbine engine 20. An electric control unit 76 may be used to control operation of a motor 50, which may drive pump 40. Shut-off/purge valve 60 may be operated by the electric control unit 76 or may be pressure operated to provide purge air from the purge air source 46 to the gas turbine engine 20 when fuel flow is not desired. Pressure for operating the shutoff/surge valve may be provided by either the fuel or purge air supply.
One disadvantage of the above approach is the inability of system 10 to operate effectively at low fuel-to-air ratios approaching a lean stability limit, known as the blowout limit, or with high fuel turndown ratios. Under certain conditions, such as when using system 10 during idle descent of an aircraft on a cold day, the combustor of the gas generating portion of the gas turbine engine may experience fuel starvation at one or more fuel injectors. In this situation, the blowout limit may be exceeded, potentially leading to totally extinguishing the combustion process and stopping the engine's operation.
One attempt to prevent this fuel starvation problem is disclosed in U.S. Pat. No. 4,903,478 to Seto, et al. The Seto patent shows a design of a dual manifold fuel system. Fuel flow to both manifolds is controlled by a fuel controller. One of the two manifolds has an off valve interposed between it and the fuel control. One of the disadvantages of the design in the Seto patent is that it does not offer the capability of independently controlling fuel flow during transitions in engine operation or allow fuel to flow simultaneously through both manifolds to prevent blowout, optimizing combustion temperature distributions, or minimizing combustion emissions.
As can be seen, there is a need for an improved system, apparatus, and method for metering fuel in a vehicle fuel system. Furthermore, there is a need for an apparatus and method for delivering fuel to an engine that functions efficiently during engine operation at various power levels and at high fuel turndown ratios. There is a further need for a fuel system for gas turbine applications that maximizes engine operability and results in extended hot-section life and reliability.